Transcript Testing your circuit.

An introduction to PIC’s for KS3
and KS4.
Mr Rooks
Hetton School.
Peripheral Interface Controller.
PIC
• A PIC microcontroller is often described as ‘
a computer on a chip’.
PICs are widely used in every day life.
•A modern car for example can use around 40 chips for many purposes such as
controlling the management of the engine and controlling the internal temperature
of the car.
PICs are made by many companies
& are available in many different
sizes & types.
Peripheral Interface Controller.
•This Diagram shows how we can use
different inputs to control an output via the
PIC microcontroller
Peripheral Interface Controller.
•Most PICs are FLASH reprogrammable.
•This means that we can download a flowchart to tell the chip how we want it to
react to different inputs. If we make a mistake or want the PIC to react
differently then we can FLASH the chip as many times as we wish. (100,000 times)
This is what a typical
flowchart may look like.
The PIC we will be using
is the PICAXE-08 12F629
Peripheral Interface Controller.
•The first step is to build the circuit !
•What the completed circuit should look like.
•The circuit uses an LDR or a push switch as INPUTS.
•The OUTPUTS are LEDs & a piezo sounder.
Peripheral Interface Controller.
Light dependent resistor (LDR)
What is an LDR?
A Light Dependent Resistor (LDR) is
special type of resistor that reacts
to changes in light level.
The resistance of the LDR changes
from about 1,000,000 Ohms in
darkness to a few hundred Ohms in
bright light
Peripheral Interface Controller.
Using switches
A switch is used with
a resistor as shown in
the diagram. The value
of the resistor is not
that important, but a
10k resistor is often
used.
This arrangement is essential
if the device is to work reliably.
Peripheral Interface Controller.
Using piezos.
A piezo needs a constantly changing
‘on-off’ signal to make a noise.
It is very simple to set up. Simply
connect the red wire to the
microcontroller output pin and the
black wire to 0V (ground).
(You can use a speaker instead but
you will need to include extra
components in the circuit)
Peripheral Interface Controller.
LEDs - Light Emitting Diodes
What is an LED?
An LED is a semi-conductor
device that gives off light
when a current is passed
through it.
L.E.Ds come in many different
sizes, colours and shapes.
They need around 20mA of
current to light them up, this
means they can be driven
directly from the chip.
This is the arrangement of
the LED from the PIC chip.
The cyberpet
Today, you will build a working cyberpet.
This device will have eyes and a voice.
It will respond to touch and even react when you come close.
The cyberpet
Schematic Diagram
Testing your circuit.
Step 1 - Check the solder joints.
Check that all the joints are connected to both the pad and the wire, and that
the wire is held firmly so that it does not 'wobble' when pulled.
Also check that the solder does not accidentally bridge between two pads. This
is most likely to happen on the LEDs, the LDR and on the piezo.
On the stereo socket the two square pads close together on each side can be
joined as they are already joined by a track on the board. However they must not
be joined to the central round hole.
Step 2 - Check the components.
Check that the black battery clip wire is in the hole marked 'OV' and the red
battery clip wire is in the hole marked 'V+‘
Check that the PICAXE-08 chip is in the socket correctly, with the dent
(showing pin1) closest to the stereo socket.
Check that the flat edge of the LED is connected to the correct hole on the
PCB.
Testing your circuit.
Step 2 - Check the components. (Cont)
Make sure you have not forgotten the wire link over the holes marked PX at the
bottom left of the board.
Make sure the brass side of the piezo is stuck down with a sticky pad.
Check that the socket is correctly soldered, including the middle square pad
which is often forgotten by mistake.
Testing your circuit.
Step 3 - Connect the battery.
Check that the 3 AA batteries are in the battery box the correct way around.
Connect the battery box to the battery snap and put the back of your finger on the
PICAXE chip.
If it starts to get hot remove the battery box immediately because there is a
problem –
most likely that the chip or the battery snap wires are around the wrong way
Programming - Drawing Flowcharts
Flowcharts are a useful tool that allow programs to be drawn graphically to
make them easier to understand.
These flowcharts are then automatically converted ready for download into
the PICAXE.
Step by Step Guide on Drawing Flowcharts
1) Start the PIC Logicator 2005 software.
2) Select PIC > select PIC type.
3)Select PICAXE-08
4) Check that the 'Serial Port' is set to
COM 1 for this work today
Programming - Drawing Flowcharts
5) Set the chip to have 3 outputs – it will automatically set the remaining pins
to inputs
6) Draw the flowchart by dragging the correct symbols onto the screen, and
then using the mouse to draw arrows between the symbols.
7) Once the flowchart is complete it can be tested on screen then downloaded
into the PICAXE by clicking the ‘Yellow lightening bolt’.
The first line of programming
Testing your circuit.
Download a program to test LED 0.
LED 0 can be tested by a simple program like this:
Look back at the
schematic diagram
of the Cyber pet to
clarify what is
meant by LED 0
It will switch the LED (connected to output pin 0) on and off every second.
Testing your circuit.
Test the other LED
Repeat the program in step 4, but use high 4 and low 4 instead of high 0 and low 0.
This will test the other LED.
Note that there is no need to re-write the programme.
Just double click on each of the cells then click on the appropriate output number.
If you leave o/p 0 at a ‘1’ and change o/p 4 to a ‘1’, both LED’s will flash when the
programme is downloaded.
Testing your circuit.
Test the piezo
The piezo it can be tested by a simple
program like this:
Drag ‘SOUND’ boxes in.
This program will make the piezo,
connected to output pin 2, make 4
different sounds.
The notes are chosen at random and
each lasts 1 second
Testing your circuit.
If the piezo does not work at all, check:
The correct output pin number is being used in the program
All the solder joints are good
That the wire link over the letters PX is on the board
Testing your circuit.
Step 7 - Test the switch
This next program will switch ‘output 0’ on for two seconds
after the switch has been momentarily pressed. It will then
switch ‘output 0’ off again and return to the main loop.
When working, experiment with the switch pressed on for
longer periods and observe the effect
Testing your circuit.
Enter the program
shown opposite and
download to your
circuit
Testing your circuit.
Step 8 - Test the LDR
This is a simple test which uses the LDR as if it were a switch.
In bright light, a high voltage nearly equal to that of the battery will be at
the input pin and the microcontroller will ‘see a 1’
When dark, the voltage at the pin drops to nearly 0V and the
microcontroller ‘sees a 0’
Enter the program shown below and download it to your circuit.
You have now completed a series of focused practical
tasks.
These individual tasks have improved your skills in the
following areas:
Component recognition
Circuit board assembly
Soldering
Testing
Programming